The present invention relates to the photographic enlarger to project a specific frame of a microfilm on a sensitized material for exposure and to print out the image in a desired size, and is concerned with the method and apparatus to position the said image on the holder to which the image is held so as the frame projection is positioned precisely and automatically on the said sensitized material surface. None of the automatic positioning methods practiced so far for enlarged projection of a specific frame image of microfilms on a sensitized material surface such as printing plates is precise enough to be used, for example, to color printing, for which a multiple number of discrete images in different colors are combined. Most of the images now reproduced as printed matters by enlarged projection on printing plates are in mono-color and low accuracy in positioning causes no problems. If the enlarging reproduction is applied to multi-color printings, however, low accuracy in positioning results in a deviation between the printed images on respective color printing plates, which in turn brings about unseemly color shears on the printed picture making it unuseful. That is to say, the conventional positioning method meets the requirements for mono-color printing but does not provide the accuracy required for the preparation of color printing plates.
One of the approaches to color printing is to detect a register mark provided outside the effective image area of a specific frame directly at the position of the microfilm and to locate the projected image at the specific position on the sensitized material surface.
This method, however, has a difficulty in positioning since a micro-sized register mark on the microfilm is detected directly, and has a disadvantage in that the error in positioning the projected image is also enlarged proportionally to the magnification.
For color printing, the required positioning accuracy on the sensitized material surface is on the order of 0.03 mm, which means the direct positioning accuracy of the register mark outside the effective area of a specific frame image must be 0.003 mm, if the magnification is 10 times, and such a degree of accuracy is rather hard to realize from a technical point of view.